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Abstract The examination of mechanical and wettability properties of commercial pure titanium (CP-Ti) introduced a novel challenge. The microstructure of samples was analyzed by using OM and SEM micro-images. In this study, the hardness of the surface and cross section of samples was evaluated, and the effect of several surface mechanical attrition treatments (SMATed) on samples was examined. Also, the tensile test was done to compare the effect of SMAT duration on mechanical properties of samples. The contact angle method was then employed to investigate the impact of SAMT duration on the wettability trend. According to results, as the treatment time increases, twins become evident in the deeper layers of the samples. In contrast, the near-surface twins are shorter than those found in the deeper material, signifying the presence of finer grains. Moreover, the elevated hardness in SMATed samples can be attributed to several key factors, including cold work, a rise in defects and twins, and grain refinement. The surface hardness increases across the sample series (up to Ti6) due to the substantial energy input. Nevertheless, it is anticipated that further continuation of the process will result in a constant surface hardness. The increased strength observed in SMATed samples can be attributed to factors such as reduction in grain size and the formation of twins. The wettability results show that the treated surfaces exhibited a significant change in wettability compared to the untreated samples, with a 25% reduction in the contact angle. This is attributed to the surface modifications induced by the treatment process, which introduced more hydrophilic functional groups. The results also show that after 4 h of treatment, the contact angle increases, suggesting that the trend may plateau with additional treatment time.

Cyclic bending under tension (CBT) has been shown to increase room temperature elongation-to-failure in various sheet metals beyond that of simple tension. A greater understanding of deformation mechanisms in CBT would allow for its elongation-enhancing effects to be more fully exploited, creating potential for new forming strategies. CBT-induced cyclic bending/unbending stresses combined with applied macroscopic tensile stresses create complex through-thickness stress profiles, where differing hardening behavior is expected near the surfaces compared with the middle of the sheet. This work uses high resolution electron backscatter diffraction characterization of geometrically necessary dislocation density together with X-ray diffraction-based evaluations of total dislocation density and in-plane digital image correlation to provide an in-depth analysis of through-thickness dislocation development and associated hardening rates throughout the CBT process in CP-Ti Grade 4 sheet metal. It was found that dislocation density is relatively uniform across the sheet at lower cycles, increases in the sheet center at higher cycles, and eventually approaches saturation near failure. Namely, dislocation accumulation occurs more slowly in the ratcheting, bending/unbending portions of the sheet (i.e., near the surfaces) from cyclic load reversals, and develops faster in the central tensile portion, where dislocation density up to 1.43x higher than near the surfaces was observed. High dislocation densities in the sheet center were found to precede significant central void accumulation, concentrating damage away from peak surface stresses, presumably contributing to delayed failure.

This paper describes a study into the evolution of damage in commercial-purity titanium (CP–Ti) sheets subjected to cyclic bending under tension (CBT) and uniaxial tension (simple tension, ST). Sections were taken from sheets that were strained to various levels under both methods and were imaged using X-ray computed tomography (XCT) to reveal insights into the size, density, and distribution of microvoids in the sheets. Digital image correlation (DIC) was also used to observe the surface strain of CBT and ST sheets during testing. These results showed that elongation to failure (ETF) for CBT deformation is about 2.5× higher than for ST, local longitudinal strains in the bulk of the CBT sample are around 1.3× higher than the peak strain in the ST necked region, and 1.7× higher in the localized region of CBT failure. It was found that the volume-density of voids in both sheets followed a similar exponential increase with strain, reaching nearly 45× higher in the CBT than the ST sheets before the onset of failure, mainly due to the higher strain levels achieved. A higher volume density of voids developed in the center of sheets at high levels of strain, for both processes, with the density in the sheet center becoming approximately double that found near the edges. Scanning electron microscopy (SEM) was used to examine the fracture surface of CBT and ST sheets after failure. The observations are presented and discussed highlighting the CBT process as effective to delay ductile fracture of the CP-Ti sheets.

Fatigue failure is invariably the most crucial failure mode for metallic structural components. Most microstructural strategies for enhancing fatigue resistance are effective in suppressing either crack initiation or propagation, but often do not work for both synergistically. Here, we demonstrate that this challenge can be overcome by architecting a gradient structure featuring a surface layer of nacre-like nanolaminates followed by multi-variant twinned structure in pure titanium. The polarized accommodation of highly regulated grain boundaries in the nanolaminated layer to cyclic loading enhances the structural stability against lamellar thickening and microstructure softening, thereby delaying surface roughening and thus crack nucleation. The decohesion of the nanolaminated grains along horizonal high-angle grain boundaries gives rise to an extraordinarily high frequency (≈1.7 × 103 times per mm) of fatigue crack deflection, effectively reducing fatigue crack propagation rate (by 2 orders of magnitude lower than the homogeneous coarse-grained counterpart). These intriguing features of the surface nanolaminates, along with the various toughening mechanisms activated in the subsurface twinned structure, result in a fatigue resistance that significantly exceeds those of the homogeneous and gradient structures with equiaxed grains. Our work on architecting the surface nanolaminates in gradient structure provides a scalable and sustainable strategy for designing more fatigue-resistant alloys.

The grain refinement and texture regulation mechanism of spin-formed commercially pure titanium (CP–Ti) cathode during annealing were studied by electron back scatter diffraction (EBSD) and transmission electron microscopy (TEM). The results show that the CP-Ti is seriously deformed after spinning, and the internal strain forms are mainly tension in spinning direction (SD), compression in normal direction (ND), and shear in transverse direction (TD). The dynamic recrystallization occurs during the spinning process, and the recrystallization nucleation mechanism is mainly subgrain nucleation. When spin-formed CP-Ti is annealed at 500 °C, the well-defined substructures generated by fragmentation of primary grains during deformation, as well as the cellular substructures formed by rearrangement of high-density entangled dislocations during annealing can evolve into a large number of fine equiaxed and randomly oriented recrystallized grains. In this case, the subgrain nucleation-dominated recrystallization nucleation mechanism can significantly refine grains. When annealed at 560 °C, a large number of tongue-shaped nuclei with similar orientation to the original grain generated at the grain boundaries, the recrystallization nucleation is inferred to be dominated by grain boundary bulge mechanism. Different recrystallization nucleation mechanisms result in different annealing texture evolution behaviors. When annealed at 500 °C, in the rapid nucleation stage of recrystallization (before 30 min), the texture strength is gradually weakened due to many randomly oriented recrystallized nuclei. With increasing the time from 30 min to 60 min, the recrystallization nucleation and growth reach a dynamic equilibrium, the texture strength tends to be stable. When annealed at 560 °C, a large number of recrystallized grains with similar orientation to the original deformed grains are formed. Oriented nucleation results in a strong texture at the short annealing time (5 min), but the competitive growth of different orientations makes the texture strength gradually decrease with the prolongation of annealing time. In any case, the overall texture strength annealed at 560 °C is higher than that annealed at 500 °C under the same annealing time.

It is important to precisely polish the inner surface of medical-grade TA1 pure titanium capillary tubes in order to reduce sample residue and enhance capillary pipetting precision, ultimately improving the accuracy and reliability of in vitro diagnostic equipment. To address the subpar inner surface quality of TA1 capillary tubes and the challenges associated with titanium material polishing, a novel chemically-assisted magnetic compound fluid polishing method was proposed. This method combines oxidation and mechanical removal to efficiently and precisely polish the inner surface of the tubes. Experimental studies were carried out to examine the effects of iron powder mass, hydrogen peroxide concentration and malic acid concentration on both the material removal rate and the inner surface roughness, with the aim of determining the optimal polishing parameters. The study involved the examination of surface morphology and elemental changes on the inner surface of capillary tubes both before and after polishing. This analysis aimed to assess the overall impact of the polishing technique on the inner surface of pure titanium capillary tubes. The results indicated that following a 90-minute polishing process under the specified conditions of 2 mg of iron powder, a hydrogen peroxide concentration of 7.2% and a malic acid concentration of 6%, the surface roughness of the TA1 capillary tube decreased from Ra 675 nm to Ra 75 nm. In the well-polished area devoid of initial dents, the surface roughness reached Ra 19.5 nm, with a material removal depth of up to 28 μm. Furthermore, the original surface scratches were effectively eliminated, both the depth and width of dents were significantly reduced, and no additional elements were introduced during the polishing process.

The effect of microstructure and mechanical properties of submicro grained commercial pure titanium (CP–Ti) on the wear mechanism is still unclear. In the present work, CP-Ti samples were subjected to multi-axial forging (MAF) and low-temperature annealing treatment to prepare ultrafine-grained (UFG) material. The mechanical properties, microstructure, and tribological characterization between coarse-grained (CG) sample and UFG samples were comparatively studied. The results showed that the MAF sample could reach a grain size of 165 nm, while its grains coarsened slightly after low-temperature annealing. The MAF sample had the highest strength and hardness and the lowest coefficient of friction, but only a 7.3 % decrease in wear rate compared to the CG sample. The 400 °C annealed MAF sample possessed a good combination of tensile strength (814 MPa) and elongation (18.6 %), resulting in the lowest wear rate of 16.8 × 10−5mm3/(N∙m). The dominated wear mechanisms of the CG sample, MAF sample and 500 °C annealed MAF sample were abrasive wear, adhesive wear and delamination wear, while the primary mechanism of the 400 °C annealed MAF sample was abrasive wear and adhesive wear. It was found that the wear mechanism transforming, higher hardness and sufficient work hardening could be responsible for lower wear rate of the 400 °C annealed MAF sample. The 400 °C annealed MAF sample showed a thinner and more homogeneous deformation layer near the worn surface, and its thickness of deformation layer was about 8 μm.

Modeling concurrent nucleation and growth in the phase-field framework on experimentally relevant length scales remains a significant challenge due to spatial resolution and driving force limitations. This work proposes a modeling framework that overcomes these challenges by integrating the explicit nucleation method within the recently developed high-driving force phase-field model to investigate the influence of the cooling rate on solid-state nucleation and growth. The model accurately captures the growth behavior of individual nuclei across varying length scales, and allows efficient one grid point nucleation without modifying the high driving force equation. To accommodate nanoscale nucleation within a mesoscale phase-field framework, the model incorporates an analytical subscale step accounting for critical nucleus growth to one grid point. The model was applied to the β to α transformation in extra pure titanium, for which a material-specific input parameter study was performed. Simulation results were compared to experimental results on the cooling rate dependence of transformation temperatures and mean grain sizes obtained through an Electron Backscatter Diffraction analysis of furnace-, air-, and water-cooled samples. The model's significance lies in extending the phase-field method's applicability to simulate nucleation on much larger length-scales than previously achievable, bridging the gap between simulation and experimental length-scales.

In order to investigate the effect of porosity on the comprehensive performance of bioactive coatings， a TiO2 coating was prepared on the surface of TA2 pure titanium using micro-arc oxidation.By varying the concentrations of Na2B4O7 and NaOH in the electrolyte， the effects of electrolyte composition on the phase composition， microstructure， hardness， thickness and hydrophilicity of the micro-arc oxidation coating were examined under constant current mode.Results showed that the coating phase was primarily rutile TiO2.The phase composition， morphology， thickness， hardness and wear resistance of the coating were significantly affected by the concentrations of sodium hydroxide and sodium tetraborate.Moderate addition of NaOH can enhance the thickness， porosity， hardness， wear resistance and corrosion resistance of the coating.However， when the concentration of sodium hydroxide was too high， porosity decreased and coating performance was reduced.When the electrolyte formula was 0.15 mol/L NaOH and 0.10 mol/L Na2B4O7， a porous coating with a "trabecular bone-like" structure was prepared， exhibiting high porosity and good comprehensive performance.

Abstract Fatigue failure is invariably the most crucial failure mode for metallic structural components. Most microstructural strategies for enhancing fatigue resistance are effective in suppressing either crack initiation or propagation, but often do not work for both synergistically. Here, we demonstrate that this challenge can be overcome by architecting a gradient structure featuring a surface layer of nacre-like nanolaminates followed by multi-variant twinned structure in pure titanium. The polarized accommodation of highly regulated grain boundaries in the nanolaminated layer to cyclic loading enhances the structural stability against lamellar thickening and microstructure softening, thereby delaying surface roughening and thus crack nucleation. The decohesion of the nanolaminated grains along horizonal high-angle grain boundaries gives rise to an extraordinarily high frequency (≈1.7 × 103 times per mm) of fatigue crack deflection, effectively reducing fatigue crack propagation rate (by 2 orders of magnitude lower than the homogeneous coarse-grained counterpart). These intriguing features of the surface nanolaminates, along with the various toughening mechanisms activated in the subsurface twinned structure, result in a fatigue resistance that significantly exceeds those of the homogeneous and gradient structures with equiaxed grains. Our work on architecting the surface nanolaminates in gradient structure provides a scalable and sustainable strategy for designing more fatigue-resistant alloys.